This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. SPECIFIC AIMS 1) To determine whether the insulin sensitivity index derived from a frequently sampled intravenous glucose tolerance test will be greater with testosterone replacement compared to estrogen replacement. 2) To determine whether an increase in testosterone levels is a significant predictor of insulin sensitivity in older men when accounting for central adiposity.